It has been recognized by physicians that it is extremely important to continuously monitor cardiac patients immediately following coronary attacks. Such is normally accomplished very effectively in the coronary care unit of most American hospitals where the patients are continuously monitored following heart attacks to detect arrhythmias of the heart, particularly warning ventricular arrhythmias which may lead to ventricular fibrillation and death. Through prompt recognition and treatment of these warning ventricular arrhythmias in coronary care units, the mortality rate of acute myocardial infarctions has been reduced by one half. In addition, approximately 15% of post myocardial infarction cardiac patients continue to have frequent ventricular extra systoles (more than 20 per hour) after discharge from the hospital and while in an out-patient status.
This experience has led physicians to the recognition that it is desirable to continue such direct intensive monitoring of the high risk cardiac patient's ECG signals subsequent to release from the cardiac care unit. Constant monitoring of these patients after release from the hospital is difficult because of the logistics involved and particularly since they can no longer be monitored closely as a group by direct wiring or close telemetry such as is possible in a hospital. As a result, various systems have been developed to attempt to monitor the ECG signals of out-patients to thereby provide a diagnostic tool for additional treatment or variation of treatment for the patients as may be required.
The systems currently in existence for such out-patient ECG signal monitoring basically fall into four main types, which are, portable tape recorders, telephone transmission devices, radio transmission devices, and tape recorders which use telephone transmission. While each of these devices operates quite well, there are in each of the systems disadvantages and limitations which preclude safe, close and continuous monitoring of the ECG signals generated by the out-patient. Since the warning ventricular arrhythmias which lead to ventricular fibrillation may develop at any time and without prior indication and, in fact, sometimes without the patient even recognizing such is occurring, that is, no physical symptoms are immediately present, it is apparent that the patient may expire during the time when the cardiac signals are being recorded but are not to be soon reviewed.
The typical portable tape recorder systems currently in existence must be worn continuously by the patient for the period of time for which they are designed to record typically 12 to 26 hours. The device weighs from one to two pounds and thus is relatively heavy and uncomfortable to the patient. Subsequent to the time during which recording occurs, the recorder is returned to the medical facility by the patient where the tape can be removed and the device can be placed in condition for a new recording. The recorded tape is then analyzed and a report thereon is transmitted to the attending physician who can then decide further activity or treatment as may be required. Obviously, such devices result in a delayed data retrieval and analysis in that the tapes are returned only subsequent to the predetermined recording period (between 12 and 26 hours). In addition, there is a further delay while the patient returns the tape recorder to the scanning facility, the scanning facility analyzes the recording, compiles a report and transmits it to the physician. Thus, during the time when recording ceases and until the tape is removed, no recordation of the ECG signal is being made. As can also be seen, these devices have a severe distance limitation in that the recording must be scanned at a specialized medical facility and thus is impractical for patients who live long distances from such facility.
As further evidence of the limitations of these devices reference is made to the January, 1977 issue of Circulation, An Official Journal of the American Heart Association, Inc., Volume 55, No. 1, page 210 and 211; and to the May 26, 1977 issue of The American Journal of Cardiology Volume 39, pages 873-879; and to the May 1972 issue of Archives of Internal Medicine, Volume 129, pages 773-779. These three articles report deaths occurring from ventricular fibrillation while the patient was wearing a tape recorder.
Some of the telephone transmission devices are designed in such a way that they will automatically detect a warning arrhythmia and sound an alarm to thereby alert the patient. The patient is then expected to telephone the medical facility to transmit the ECG signals which have been converted to a frequency modulated signal within the audio range of the telephone. Some of the devices do not have an automatic arrhythmia detection system but instead depend upon the patient recognizing a symptom such as palpitations, chest pain, shortness of breath or lightheadedness which may be caused by the warning arrhythmia. If the patient recognizes the symptom, the patient then dials the medical facility and transmits the signal by telephone. These telephone transmitting devices have a number of shortcomings. It is obvious that the warning arrhythmias causing the symptoms or the automatic alert to occur are missed because the medical facility can only begin to record once the patient has completed the call. Thus the medical facility only begins to record subsequent to the occurrence of such warning arrhythmias. It is obviously also impractical for the patient to maintain the telephone contact with the medical facility for longer than a few minutes time during which the patient must remain by the telephone. Thus only a very small amount of ECG signal data is, in fact, ever received or recorded by the medical facility. As above noted often a patient will not recognize the symptoms of a warning arrhythmia and thus this warning arrhythmia may never be recorded. In addition the patient may be incapacitated by the arrhythmia or already unconscious and thus is unable to complete a telephone call and may expire prior to any data being transmitted to the medical facility. Furthermore, if the patient's ECG signals are to be transmitted for any substantial period of time the telephone lines at the patient's home and the medical facility may be tied up for substantial periods which adds to inconveniences as well as tremendous expense.
The radio transmission devices again operate upon the principle of detecting arrhythmias through the use of electronic logic networks. When such occurs the radio transmission capability is actuated and the ECG signals are transmitted through the use of a UHF or VHF radio transmission to a central medical facility capable of recording and analyzing the signals. Obviously, these devices suffer from distance limitations in that the radio transmissions are typically line of sight and may also have tremendous reliability problems in that the UHF and VHF signals may be disturbed as a result of concrete-steel construction which may exist between the patient and the central receiving facility. There are also only a limited number of radio channels allotted to this type of transmission which automatically limits the number of patients capable of being monitored within the receiving range of any medical facility. Furthermore, the problem with respect to incomplete data retrieval as above-described is also inherent in a system of this type. In addition, the radio transmission devices as well as the telephone transmission devices which have the automatic detection systems therein, suffer from the additional problem in that the signals which cause the activities of the system are typically warning arrhythmias. These devices allow no way to quantitate total heartbeats or to detect trends which reflect the rate or QRS morphology changes. These latter provide information supplemental to the detection of arrhythmias which information is significant to a physician treating a high-risk cardiac out-patient. Furthermore, there is no way to tell what warning arrhythmias are not being detected by the electronic logic in the radio transmission devices and, in fact, significant arrhythmias may be missed which cannot be verified because only limited portions of the ECG signal are being retrieved.
Where the portable tape recorder is utilized along with the telephone transmitter system, one can immediately ascertain that the incomplete data retrieval above referred to exists in addition to the tying up of telephone lines both at the patient's home and at the medical facility. In addition thereto, one skilled in the art will recognize that by continuously recording, rewinding and replaying the recorded information on the tape less than one-half of the patient's ECG signal history is being recorded and transmitted. If the patient is required to frequently record and play back, for example, in ten minute intervals, it will immediately also be seen that the patient is constantly calling the medical facility every 20 minutes to transmit his 10 minute recorded signal. Such would mean that he would be telephoning the medical facility approximately 72 times through a 24 hour period which, obviously, becomes impractical for a high-risk cardiac out-patient.
The best prior art known to applicant is described in the following U.S. Pat. Nos. 3,199,508; 3,212,496; 3,267,934; 3,434,151; 3,603,881; 3,650,263; 3,724,455; 3,742,938; 3,768,017; 3,779,237; 3,832,994; 3,639,907; 3,880,144; 3,882,277; 3,893,453; 3,972,320; 3,910,260; 3,934,267; 3,946,744; 3,951,135; 3,958,563; 3,986,498; 3,991,747; 3,913,567.